For many years, petroleum and/or natural gas has been recovered from subterranean reservoirs by using drilled wells and production equipment. Oil and natural gas are found in, and produced from, porous and permeable subterranean formations, or reservoirs. These subterranean formations are referred to as “hydrocarbon formations” as typically oil and gas are found in proximity to each other underground. The porosity and permeability of the formation determine its ability to store hydrocarbons, and the facility with which the hydrocarbons can be extracted from the formation.
When selecting/using a fluid to be used in the treatment of an oil and/or gas well, it is important for the fluid to have the right combination of additives and components to achieve the necessary characteristics of the specific end-use application. A primary goal amongst many aspects of hydrocarbon formation treatment is to optimize recovery of oil and/or gas from the formation. In some circumstances, surfactant solutions or microemulsions are chosen to treat a hydrocarbon formation for variable technical reasons. However, in part because the microemulsion used during the operation of an oil and/or gas well are often utilized to perform several tasks simultaneously, achieving necessary to optimal characteristics of the treatment fluid is not always easy.
Micelles
Micelles are typically defined as a supramolecular assembly of surfactant molecules dispersed in a liquid medium wherein the surfactant molecules are comprised of a dual structure where one portion of the surfactant molecule is considered hydrophilic (water loving, polar) and another portion of the molecule is considered hydrophobic (lipophilic, fat or oil loving).
Surfactants can be organized into different classes including anionic, cationic, non-ionic, and amphoteric. All classes include this relative hydrophilic/hydrophobic dual nature. When dispersed in water in favorable conditions of concentration and temperature, micelles of surfactants may form where hydrophilic “head” regions are in contact with the surrounding aqueous solvent, sequestering the hydrophobic molecular regions in the micelle center away from water.
A micellar fluid may be described as a fluid performing a specific function or combination of functions where one function is performed by such micellar supramolecular assemblies that may comprise: surfactant molecules of single or multiple classes, co-solvents, oil phase materials, and preferably brine-resistant colloidal particles utilizing a hydrophilic or a combination of hydrophilic and hydrophobic surface functionalization on the particle surface.
Microemulsions
In contrast to “micellar fluids” microemulsions are described as clear, thermodynamically stable, isotropic liquid mixtures of oil phase, water phase, and surfactant, frequently in combination with a cosurfactant or cosolvent. The aqueous phase may contain salt(s) and/or other ingredients, and the oil phase may be a complex mixture of different hydrocarbons and olefins.
In contrast to ordinary emulsions, microemulsions form upon simple mixing of the components and do not require the high shear conditions generally used in the formation of ordinary emulsions.
The three basic types of microemulsions are
(A) direct (oil dispersed in water, o/w),
(B) reversed (water dispersed in oil, w/o), and
(C) bi-continuous.
Typical dispersed domain diameter in a microemulsion may be approximately 1-100 nm and more typically 1-50 nm, the small domain size contributing to optical clarity.
In contrast to a microemulsion, a micellar fluid may not be clear, thermodynamically stable, isotropic, or contain an oil phase. A micellar fluid may have dispersed domain sizes in excess of 50 nm and may contain other phases of materials within or at the surface of the dispersed domain such as brine-resistant colloidal silica (solid phase).
The use of treatment (aka “remediation”) microemulsions to recover oil and gas from hydrocarbon formations that have a reduced output is well known. Several different types of fluid mixtures have been disclosed in the prior art for improving oil recovery in hydrocarbon-bearing subterranean formations in remediation, fracturing, stimulation, completion, and production.
U.S. Pat. No. 3,981,361, “OIL RECOVERY METHOD USING MICROEMULSIONS”, issued 21 Sep. 1976, describes and claims a method for recovering oil from subterranean formations using microemulsions. The fluid is compounded from an oil, an aqueous medium, and a surfactant, and its parameters are varied to form volumetric ratios of oil to surfactant in the fluid and/or water to surfactant in the fluid greater than 0.5. Preferably, the volumetric ratios will be greater than 2.0. Among the parameters which can be adjusted to change these volumetric ratios include the salinity of the aqueous medium, the temperature of the fluid system, the chemical structure of the surfactant, the chemical structure of any cosurfactant included in the fluid, the degree of aromaticity of the oil, and composition of dissolved solids in the aqueous medium. In one preferred embodiment of the invention an oil is chosen which has physical and chemical characteristics substantially the same as the formation oil. The aqueous medium has physical and chemical characteristics substantially the same as the formation water. A surfactant which has a chemical structure which will form a fluid having volumetric ratios of oil to surfactant and/or of water to surfactant greater than 0.5 is selected for inclusion in the fluid system. The oil; aqueous medium; and surfactant, determined in accordance with the teachings of this invention, form a class of microemulsion which is effective in recovering oil from subterranean formations of interest. All microemulsions within the class will be effective for recovering oil from the formation. Oil is recovered by compounding a fluid within the class and injecting this fluid into the formation.
U.S. Pat. No. 3,885,628, “RECOVERY OF OIL USING MICROEMULSIONS”, issued 27 May 1975, describes and claims the recovery of crude oil in a subterranean formation through the injection of at least one phase formed from a composition within the multiphase region of an oil-water-surfactant ternary diagram. One embodiment includes the injection of two or more mutually immiscible phases which would be in phase equilibrium within the multiphase region in the ternary diagram of a fluid system, at least one of the phases being a fluid. Low interfacial tensions exist between the immiscible phases in equilibrium. Where one of the phases in equilibrium comprises predominantly oil or predominantly water, in a further embodiment the fluid phase in equilibrium therewith can be injected alone to achieve efficient crude oil recovery. Where there are three phases in equilibrium, one of which comprises predominantly oil and another comprises predominantly water, in a further embodiment the remaining fluid phase in equilibrium therewith can be injected alone to achieve efficient crude oil recovery.
U.S. Pat. No. 4,240,504 “SIMULTANEOUS MICROEMULSION-AQUEOUS PHASE FLOODING PROCESS”, issued 23 Dec. 1980, describes and claims a method of enhanced oil recovery wherein an upper-phase or a middle-phase fluid and an immiscible aqueous phase are simultaneously injected into a subterranean formation. The viscosities of the injected phases are adjusted so that the aqueous phase/fluid viscosity ratio approximates the reservoir brine/oil viscosity ratio. The injection rates of the injected phases are such that similar oil, fluid and aqueous phase velocities are achieved in the reservoir. Oil is displaced to a production well and recovered.
U.S. Pat. No. 7,380,606, “COMPOSITION AND PROCESS FOR WELL CLEANING”, issued 3 Jun. 2008, describes and claims a well treatment fluid that is formed by combining a solvent-surfactant blend with a carrier fluid. In preferred embodiments, the solvent-surfactant blend includes a surfactant and a solvent selected from the group consisting of terpenes and alkyl or aryl esters of short chain alcohols. The disclosed well treatment fluid can be used in well remediation, stimulation and hydrogen sulfide mitigation operations. Additionally, the well treatment fluid can be used in the production of benzothiophenes through interaction with hydrogen sulfide.
U.S. Pat. No. 8,101,812, “Extraction of Hydrocarbons from Hydrocarbon-Containing Materials”, issued on 24 Jan. 2012, describes and claims a method of extracting hydrocarbon-containing organic matter from a hydrocarbon-containing material, comprising the steps of: providing a first liquid consisting essentially of a turpentine liquid alone or a combination of a turpentine liquid and a turpentine-miscible second liquid wherein the ratio of said turpentine liquid to said turpentine-miscible liquid is greater than or equal to 1:1; contacting a hydrocarbon-containing material with said first liquid to form an extraction mixture; extracting said hydrocarbon material into said turpentine liquid; and separating said extracted hydrocarbon material from a residual material not extracted.
U.S. Pat. No. 8,272,442, “In Situ Extraction of Hydrocarbons From Hydrocarbon-Containing Materials”, issued on 25 Sep. 2012, describes and claims a method of extracting hydrocarbon-containing organic matter from a hydrocarbon-containing material, comprising a viscous liquid, liquid or gaseous fossil fuel material selected from heavy crude oil, crude oil, natural gas, or a combination thereof, the method comprising: providing a hydrocarbon-extracting liquid consisting essentially of turpentine liquid alone or a combination of a turpentine liquid and a turpentine-miscible second liquid; contacting heavy crude oil, crude oil, natural gas, or a combination thereof in-situ in an underground formation containing said fossil fuel material, with said hydrocarbon-extracting liquid, to form an extraction mixture so as to extract hydrocarbon-containing organic matter from said heavy crude oil, crude oil, natural gas, or a combination thereof into said hydrocarbon-extracting liquid and form an extraction liquid; removing said extraction liquid from said formation, the extraction liquid comprising said turpentine liquid containing the extracted hydrocarbon-containing organic matter; and separating said extracted hydrocarbon-containing organic matter from a residual material not extracted.
U.S. Pat. No. 8,404,107, “Extraction of Hydrocarbons from Hydrocarbon-Containing Materials”, issued on 26 Mar. 2013, describes and claims a method of extracting hydrocarbon-containing organic matter from a hydrocarbon-containing material using a homogenous one-phase hydrocarbon-extracting liquid consisting essentially of a turpentine liquid, comprising the steps of: contacting the hydrocarbon-containing material with a homogenous one-phase hydrocarbon-extracting liquid consisting essentially of a turpentine liquid to form a homogeneous one-phase extraction mixture and a residual material, the homogeneous one-phase extraction mixture comprising at least a portion of the hydrocarbon-containing organic matter extracted into the turpentine liquid, the residual material comprising at least a portion of non-soluble material from the hydrocarbon-containing material that are not soluble in the turpentine liquid; separating the extraction mixture from the residual material; and separating the extraction mixture into a first portion and a second portion, the first portion of the extraction mixture comprising a hydrocarbon product stream comprising at least a portion of the hydrocarbon-containing organic matter, the second portion of the extraction mixture comprising at least a portion of the turpentine liquid.
U.S. Pat. No. 8,522,876, “In Situ Extraction of Hydrocarbons From Hydrocarbon-Containing Materials”, issued 3 Sep. 2013, describes and claims a method of extracting hydrocarbon-containing organic matter from a hydrocarbon-containing material, comprising a fossil fuel material selected from oil shale, coal, sands, or a combination thereof, the method comprising: providing a hydrocarbon-extracting fluid consisting essentially of turpentine fluid alone or a combination of a turpentine fluid and a turpentine-miscible second fluid; contacting oil shale, coal, oil sands, or a combination thereof with said hydrocarbon-extracting fluid, to form an extraction or separation mixture so as to extract or separate hydrocarbon-containing organic matter from said oil shale, coal, oil sands, or a combination thereof into said hydrocarbon-extracting fluid and form an extraction fluid comprising said turpentine fluid containing the extracted hydrocarbon-containing organic matter; and separating said extracted hydrocarbon-containing organic matter from a residual material not extracted.
U.S. Pat. No. 8,685,234, “Extraction of Hydrocarbons from Hydrocarbon-Containing Materials and/or Processing of Hydrocarbon-Containing Materials”, issued 1 Apr. 2014, describes and claims a method for increasing flowability of viscous or immobile hydrocarbon-containing materials in an underground formation, flow line, or storage tank comprising contacting a hydrocarbon-containing material selected from oil (tar) sands, oil shale, natural gas, petroleum gas, heavy crude oil and/or crude oil with a non-aqueous turpentine liquid in an underground formation, flow line, or storage tank; forming a mixture of non-aqueous turpentine liquid and hydrocarbon-containing material having decreased viscosity; and causing said mixture to flow as a one-phase liquid in said underground formation, flow line, or storage tank; and wherein said non-aqueous turpentine liquid comprises α-terpineol, .β-terpineol, or a combination thereof.
U.S. Pat. No. 9,181,468, “Extraction of Hydrocarbons from Hydrocarbon-Containing Materials and/or Processing of Hydrocarbon-Containing Materials”, issued 10 Nov. 2015, describes and claims a method for increasing flowability of viscous or immobile hydrocarbon-containing materials in an underground formation or a flow line comprising contacting a hydrocarbon-containing material selected from oil (tar) sands, oil shale, natural gas, petroleum gas, heavy crude oil and/or crude oil with a non-aqueous turpentine liquid in said underground formation or flow line; forming a mixture of non-aqueous turpentine liquid and hydrocarbon-containing material having decreased viscosity; and causing said mixture to flow as a one-phase liquid in said underground formation or flow line, wherein said turpentine liquid comprises .alpha.-terpineol, .beta.-terpineol, or a combination thereof.
U.S. Pat. No. 9,428,683, “Methods and Compositions for Stimulating the Production of Hydrocarbons from Subterranean Formations”, issued 30 Aug. 2016, describes and claims a method comprising: selecting an emulsion or a microemulsion composition for injection into a wellbore of a well based on a determination of whether formation crude oil is produced or whether formation gas is produced by the well, wherein, when formation crude oil is produced by the well, the emulsion or the microemulsion composition is selected to comprise a terpene having a phase inversion temperature greater than 43° C., water, and a surfactant and the ratio of water to terpene is between about 3:1 and about 1:2; and wherein, when formation gas is produced by the well, the emulsion or the microemulsion is selected to comprise a terpene having a phase inversion temperature less than 43° C., water and a surfactant, and the ratio of water to terpene is between about 3:1 and about 1:2; and injecting the emulsion or the microemulsion into the wellbore.
There is a continued need to develop treatment fluids that can be used to recover more of the oil/gas remaining in a hydrocarbon formation.
One such ingredient in these treatment fluids is colloidal silica. Colloidal silica has many known industrial uses including frictionizing agents for textiles, improvement of polymeric materials including lowering Coefficient of Thermal Expansion, raising of Young's Modulus and Tensile strength, lowering % Elongation, raising electrical insulating properties and resistance to electrical breakdown voltage, production of more efficient catalyst materials, and many other useful functions. Colloidal silica can be used in its original aqueous form or be converted to nonaqueous colloidal dispersions for use in applications that do not tolerate the presence of water.
It has also been reported that colloidal silica can be used in treatment fluids for hydrocarbon formations, specifically in downhole injection treatments to hydrocarbon-bearing subterranean formations for improving oil recovery in downhole applications such as fracturing, stimulation, completion, and remediation.
U.S. Pat. No. 7,544,726 “Colloidal Silica Compositions”, issued 9 Jun. 2009, describes and claims a method of producing a stable aqueous silanized colloidal silica dispersion without the presence of any water-miscible organic solvents or optionally comprising one or more water-miscible organic solvents, if present, in a total amount of up to about 5% by volume of the total volume, said dispersion having a silica content of at least 20 wt %, said method comprising mixing at least one silane compound and colloidal silica particles in an aqueous silica sol having an S-value from 30 to 90 in a weight ratio of silane to silica from 0.003 to 0.2. It also describes and claims a stable aqueous silanized colloidal silica dispersion without the presence of any water-miscible organic solvents or optionally comprising one or more water-miscible organic solvents, if present, in a total amount of up to about 5% by volume of the total volume, said dispersion having a silica content of at least 20 wt % obtained by mixing colloidal silica particles and at least one silane compound in an aqueous silica sol having an S-value from 30 to 90 in a weight ratio of silane to silica from 0.003 to 0.2. It also describes and claims a stable aqueous silanized colloidal silica dispersion without the presence of any water-miscible organic solvents or optionally comprising one or more water-miscible organic solvents, if present, in a total amount of up to about 5% by volume of the total volume, said dispersion having a silica content of at least 20 wt % and having a weight ratio of silane to silica from 0.003 to 0.2, wherein colloidal silica particles are dispersed in a silica sol having an S-value from 30 to 90.
U.S. Pat. No. 7,553,888 “Aqueous Dispersion”, issued 30 Jun. 2009, describes and claims a method of producing an aqueous dispersion comprising mixing at least one silane compound and colloidal silica particles to form silanized colloidal silica particles and mixing said silanized colloidal silica particles with an organic binder to form the dispersion. The invention also relates to a dispersion obtainable by the method, and the use thereof.
US published patent application US2012/0168165A1 (abandoned 17 Dec. 2012), “METHOD FOR INTERVENTION OPERATIONS IN SUBSURFACE HYDROCARBON FORMATIONS” describes and claims colloidal silica being added to a fluid containing a wetting agent to enhance wetting of solid surfaces in and around the well and removing a water-block from the well. The wetting agent and colloidal silica combine to produce a wetting of the surfaces of the rock that allows recovery of the excess water near the well (water block).
US published patent application US2012/0175120 (abandoned 29 Nov. 2012), “METHOD FOR INTERVENTION OPERATIONS IN SUBSURFACE HYDROCARBON FORMATIONS”, describes and claims colloidal silica added to a fluid containing a wetting agent and the fluid is pumped down a well to enhance wetting of solid surfaces in and around the well before pumping an acid solution down the well. After acid is pumped, a fluid containing colloidal silica and wetting agent is again pumped down the well, leading to improved flow capacity of the well.
US published patent application US2010/096139A1 (abandoned 9 Oct. 2012) “METHOD FOR INTERVENTION OPERATIONS IN SUBSURFACE HYDROCARBON FORMATIONS”, describes and claim methods for improved intervention processes in a well. Colloidal silica is added to a fluid containing a wetting agent to enhance wetting of solid surfaces in and around the well, leading to improved flow capacity of the well.
US published patent application US 2016/0017204, “METHODS AND COMPOSITIONS COMPRISING PARTICLES FOR USE IN OIL AND/OR GAS WELLS”, now pending, describes a method for treating an oil and/or gas well comprising combining a first fluid and a second fluid to form an emulsion or fluid, wherein the first fluid comprises a plurality of hydrophobic nanoparticles and a non-aqueous phase, wherein the second fluid comprises a surfactant and an aqueous phase, and wherein in the fluid, a portion of the nanoparticles are each at least partially surrounded by surfactant and in contact with at least a portion of the non-aqueous phase; and injecting the emulsion or fluid into an oil and/or gas well comprising a wellbore.
The following patent applications discuss the use of a mixture of colloidal silica in combination with a wetting agent for modifying solid rock surfaces in an aqueous or hydrocarbon-based fluid for injection into a hydrocarbon formation to effect improved oil recovery.
U.S. Pat. No. 7,033,975, “Use of Surface Modified Nanoparticles for Oil Recovery”, issued 25 Apr. 2006, now abandoned, describes the use of surface-modified nanoparticles in fluids used to recover hydrocarbon from underground formations. The use of surface-modified nanoparticles in such microemulsions provides foams that are stable under pressure yet have a shorter foam lifetime than typical surfactant-stabilized foams after the pressure is released or lowered.
In the article, “Enhanced Oil Recovery by Flooding with Hydrophilic Nanoparticles” by Binshan, Ju; Tailing, Fan; Mingxue, Ma, School of Energy Resource, China University of Geosciences, Beijing 100083, P. R. China, Well-Log Research Center of Shengli Oil-Field, Dongying 257096, P. R. China, the mechanism of enhanced oil recovery using lipophobic and hydrophilic polysilicon (LHP) nanoparticles ranging in size from 10 to 500 nm for changing the wettability of porous media was analyzed theoretically. A one-dimensional two-phase mathematical model considering the migration and adsorption of LHP and wettability change in reservoir rock was proposed, and a simulator was developed to quantitatively predict the changes in relative and effective permeability of the oil and water phases and the oil recovery in sandstone after water driving. Numerical simulations were conducted to study the distribution of the particle concentration, the reduction in porosity and absolute permeability, the LHP volume retention on pore walls and in pore throats along a dimensionless distance, and oil production performance. In conclusion, oil recovery can obviously be improved by flooding with hydrophilic nanometer powders though permeability declines for the retention of nanoparticles in porous media. It is suggested that an LHP concentration ranging from 0.02 to 0.03 is preferable to enhance oil recovery.
Microemulsions prepared with D-Limonene as the oil-phase in combination with surfactants, cosolvents, and water are commercially available from Flotek under the “Stim-Oil” trademark, http://www.flotekind.com/index.php/products-and-services/item/402-complex-nano-fluid-technology-suite-stimoil-en.
It is generally well known in oilfield applications that subterranean formations contain large amounts of water containing dissolved salts such as NaCl, CaCl2, KCl, MgCl2 and others. This aqueous salt mixture is typically referred to as brine. Brine conditions for different regions and wells vary widely with different downhole conditions and lithologies. In general, micellar solution used downhole must either tolerate briny conditions or have brine-resistant properties.
Commercially available colloidal silica mixtures suitable for these micellar solutions include the nanoActiv™ HRT product line available from Nissan Chemical America, http://www.nanoactiv.com/. These products use nanosized particles in a colloidal dispersion, which allows the fluid to work by causing a Brownian-motion, diffusion-driven mechanism known as disjoining pressure to produce long efficacy in the recovery of hydrocarbons in conventional and unconventional reservoirs.
While these patent applications explore the use of colloidal silica, including aqueous colloidal silica, in downhole oilfield applications and there are commercial products containing colloidal silica available; none of these patent applications or commercial products address the utility of brine resistant colloidal silica being useful in hydrocarbon formation treatment micellar solution.